As shown in the patent document 1, this kind of an exhaust gas sampling and analysis system circulates a diluted exhaust gas that is an exhaust gas from an internal combustion engine (an engine) diluted with air in a dilution pipe and collects a part of the diluted exhaust gas flowing in the dilution pipe by the use of a sample collection pipe.
A sample collection probe to collect the diluted exhaust gas, a flow restriction valve to adjust a flow rate pressure of the collected diluted exhaust gas, an exhaust gas analysis device to analyze a component of the exhaust gas from the diluted exhaust gas, a critical venturi arranged to suck the dilution gas in the sample collection pipe at a constant total amount, and a suction pump are arranged in this order in the sample collection pipe. In addition, an atmospheric air path is connected between the exhaust gas analysis device and the critical venturi in the sample collection pipe. This arrangement makes it possible to reduce a change of a flow pressure of the diluted exhaust gas passing the exhaust gas analysis device in accordance with a ratio between an amount of the diluted exhaust gas flowing in the sample collection pipe and an amount of the atmospheric air introduced from the atmospheric air path.
However, since the total amount of the flow rate of the dilution gas in the sample collection pipe is made constant by means of the critical venturi and the suction pump, there is a problem that the flow rate of the sampled exhaust gas definitely changes if the flow rate of the atmospheric air flowing in the sample collection pipe supplied from the atmospheric air path changes. In addition, if the exhaust gas is of high pressure, the change of the flow rate becomes big. As a result, there is a problem that it is unable for the above-mentioned arrangement to cope with the change of the flow rate.
In addition, for the exhaust gas analysis device used for the exhaust gas sampling and analysis system, since a flow rate and a pressure of the sampled exhaust gas introduced into the exhaust gas analysis device are determined by a specification, it is necessary to adjust the flow rate and the pressure of the sampled exhaust gas within a range of the specification.
In order to attain this object, a pump of a constant volume type is arranged in the downstream side in a flow of the diluted exhaust gas for the exhaust gas sampling and analysis system of the above-mentioned patent document 1 and it is so configured that the total amount and the pressure of the diluted exhaust gas flowing in the dilution pipe are kept generally at a constant value respectively by means of the pump of the constant volume type even though the amount of the exhaust gas flowing in the exhaust gas introduction pipe changes. In addition, an air introduction pipe is connected to the dilution pipe and an air filter is arranged on an atmospheric air take-in port of the air introduction pipe.
However, as is clear from that the total amount and the pressure of the diluted exhaust gas flowing in the dilution pipe are kept generally at a constant value by the use of the pump of the constant volume type for the above-mentioned exhaust gas sampling and analysis system, it is not foreseen to sample the high pressure exhaust gas. In addition, since the air introduction pipe is connected to the dilution pipe and the filter is arranged on the atmospheric air take-in port, it is quite unlikely that the pressure in the dilution pipe becomes high, even though it is likely that the pressure in the dilution pipe becomes low due to clogging of the air filter.